Real-Time Multibody System Dynamic Simulation: Part I. A Modified Recursive Formulation and Topological Analysis

ABSTRACT

ABSTRACT With the advent of parallel computers and recursive dynamics formulations, multibody mechanical systems such as ground vehicles can be simulated in real time. This permits the engineer to rapidly modify design parameters, evaluate dynamic performance, and improve designs, prior to fabrication and testing. Perhaps more important, real-time simulation can be used for simulation with the operator-in-the-loop, permitting system design to be optimized for the capability of the human operator. To achieve the goal of real-time simulation, a modified recursive dynamics formulation and a topological analysis method for the formulation are presented in Part I. A parallel computational algorithm that exploits inherent parallelism in the modified recursive formulation and numerical results will be presented in Part II. By combining the topological analysis method and the parallel algorithm, an efficient general-purpose dynamic simulation method is developed for real-time simulation on shared memory parallel processors.     

An index 0 Differential-Algebraic equation formulation for multibody dynamics: Holonomic constraints

The Lagrange multiplier form of index 3 differential-algebraic equations of motion for holonomically constrained multibody systems is transformed using tangent space generalized coordinates to an index 0 form that is equivalent to an ordinary differential equation. The index 0 formulation includes embedded tolerances that assure satisfaction of position, velocity, and acceleration constraints and is solved using established explicit and implicit numerical integration methods. Numerical experiments with two spatial applications show that the formulation accurately satisfies constraints, preserves invariants due to conservation laws, and behaves as if applied to an ordinary differential equation.     

Non-Hydroxamate Zinc-Binding Groups as Warheads for Histone Deacetylases

Histone deacetylases (HDACs) remove acetyl groups from acetylated lysine residues and have a large variety of substrates and interaction partners. Therefore, it is not surprising that HDACs are involved in many diseases. Most inhibitors of zinc-dependent HDACs (HDACis) including approved drugs contain a hydroxamate as a zinc-binding group (ZBG), which is by far the biggest contributor to affinity, while chemical variation of the residual molecule is exploited to create more or less selectivity against HDAC isozymes or other metalloproteins. Hydroxamates have a propensity for nonspecificity and have recently come under considerable suspicion because of potential mutagenicity. Therefore, there are significant concerns when applying hydroxamate-containing compounds as therapeutics in chronic diseases beyond oncology due to unwanted toxic side effects. In the last years, several alternative ZBGs have been developed, which can replace the critical hydroxamate group in HDACis, while preserving high potency. Moreover, these compounds can be developed into highly selective inhibitors. This review aims at providing an overview of the progress in the field of non-hydroxamic HDACis in the time period from 2015 to present. Formally, ZBGs are clustered according to their binding mode and structural similarity to provide qualitative assessments and predictions based on available structural information.     

Linear response functions of a quasi-one-dimensional electron gas

The predictions for density-density-type response functions of a quasi-one dimensional electron gas are compared in detail for various models (Hubbard and Tomonaga model) and for various approximations (Monte-Carlo calculations, RPA and extended RPA). It is shown that RPA does not lead to intrinsic contradictions for electron densities larger than 1.5 inverse exciton Bohr radii. Even in this high-density regime local field corrections enhance spin- and density susceptibilities significantly.     

Darstellung,Eigenschaften und Kristallstruktur von Cl3(bpy)Ta  NOCH3, einem Methoxynitrenkomplex des Tantals

Synthesis, Properties, and Crystal Structure of Cl₃(bpy)Ta≡NOCH₃, a Methoxynitrene Complex of Tantalum TaCl₅ reacts in the presence of 2,2′-bipyridine with O-methyl-hydroxylamine or bis(trimethylsilyl)-O-methyl-hydroxylamine to yield the methoxynitrene complex Cl₃(bpy)Ta≡NOCH₃. The red complex decomposes only slowly at moist air. It crystallizes in the monoclinic space group C2/c with the lattice constants a = 1588.5, b = 1515.9, c = 1414.2 pm, β = 122.78°, Z = 8. The monomeric complex exhibits a distorted octahedral coordination for the tantalum atom. The methoxynitrene ligand is coordinated by a Ta? N triple bond resulting in a linear Ta≡N? O arrangement with Ta? N? O = 174.0° and distances Ta? N = 174.4 pm and N? O = 134.8 pm. v(Ta? N) is observed in the i.r. spectrum at 950 cm^?1.     

Dry friction in the Frenkel-Kontorova-Tomlinson model: dynamical properties

Wearless friction is investigated in a simple mechanical model called Frenkel-Kontorova-Tomlinson model. We have introduced this model in [Phys. Rev. B, 53, 7539 (1996)] where the static friction has already been considered. Here the model is treated for constant sliding speed. The motion of the internal degrees of freedom is regular for small sliding velocities or weak interaction between the sliding surfaces. The regular motion for large velocities is strongly determined by normal and superharmonic resonance of phonons excited by the so-called “washboard wave”. The kinetic friction has maxima near these resonances. For increasing interaction strength the regular motion becomes unstable due to parametric resonance leading to quasistatic and chaotic motion. For sliding velocities beyond first-order parametric resonance bistability occurs between the strongly chaotic motion (fluid sliding state), where friction is large and a regular motion (solid sliding state), where friction is weak. The fluid sliding state is mainly determined by the density of decay channels of m washboard waves into n phonons. This density describes qualitatively the effectiveness of the energy transfer from the uniform sliding motion into the microscopic, irregular motion of the degrees of freedom at the sliding interface. For a narrow interval of the sliding velocities we also found enhanced friction due to coherent motion. In the regime of coherent motion nondestructive interactions of dark envelope solitons occur.